I have read the mixed reviews on here and I think some people are just not informed on how to use the FreeAgent Theater+ (FAT+). Granted, its rough around the edges and not very intuiative, but in the end, you can get the desired result: browsing network shares with media and playing it back on your TV.
I did want to point out that maybe some do not realize that you need to use NETWORK shortcuts and not the "Movies" from the home landing page to reach movie shares on your network? I was able to point the (FAT+) towards my Windows Home Server, which happens to be running MyMovies.
There is no reason to open your computers or shares to guest level access, you can add the username and password of a valid account to access any network resources you have.
With MyMovies for WHS, this could not be any easier. I drop a movie I own into the WHS box, MyMovies catologs it, and then I am able to browse the WHS via the FAT+ and off I go. I get full DVD menu support without any issues. The only thing I need to work on: getting the DVD cover thumbnail and the directory named the same. I am sure a simple script could do it once MyMovies has run. Something to work on in 2010.
Be sure you are running the latest firmware for your FAT+ Mine is 1.26 as of 12/31/09. You can also find additional information here: http://forums.seagate.com/stx/board?board.id=fatheater
For AT&T Uverse customers, did you know that that network port on the back of your DVR units are LIVE? I plugged a switch into my Total Home DVR unit and have daisy chained an XBOX360, SlingBox, Seagate FreeAgent Theater+, and a BluRay player all off of the Total Home DRV.